﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Demo
{
    class Class1
    {
        static void Main(string[] args)
        {
            const float pai = 3.14f;
            Console.WriteLine("请输入园的半径");

            int r = int.Parse(Console.ReadLine());
            Console.WriteLine(pai*r*r);
            Console.Readey();
        }
    }
}
